Yes bitcoin has become great source of income nowadays and people are making good amount of money from it even by working part time so if they gets full time into it then it will surely maximize their earnings and they may have higher income in compare to their full time job.
yes you are right that bitcoin is a very good source of income because people are giving so much importance to bitcoin and the earning from bitcoin is also very high as compare to day jobs it is because people have seek so much opportunities in bitcoin due to which they does not need any real jobs.